Voyager 1, launched in 1977, has taken 35 years to reach the outer fringes of the solar system, the so called heliosphere where a plasma bubble of charged particles from the sun meets the cold edge of the space between stars.

Voyager 1 is now 11 billion miles from the sun and could reach interstellar space any day now. Their technology may seem obsolete by today’s standards, computers with 8,000 words of memory and 8-track tape recorders, but they were the first spacecraft to fully fly themselves.

“They were the first fully automated spacecraft that could fly themselves,” says Ed Stone, chief Voyager project scientist. “They were the peak of technology.”

The spacecraft are powered by nuclear reactors, and have their cameras turned off to conserve power but still have particle detectors turned on.

They also carry gold-plated discs containing multilingual greetings, music and pictures — in the off chance that intelligent species come across them.

A graphic showing Voyager 1 looking back at Earth.

The two spacecraft are still in remarkable shape and are still sending data back to earth, even surviving Jupiter’s radiation belt and the coldness of space for decades.

Launched alongside Voyager 2, the two spacecraft have set the distance record in terms of solar system exploration

It takes 17 hours for a radio signal from Voyager 1 to travel back to Earth. About 20 part time scientists analyze the data that it sends back.

“It was able to measure many things” along the journey, Stone said, “but its prime purpose was determining the interstellar spectrum of cosmic rays.”

Gold plated records aboard both spacecraft contain directions on how to get to Earth if any intelligent life can figure out how to use them.

“This is a major milestone,” he said. “This will be the first spacecraft to enter interstellar space. We’ll know exactly how big this bubble is.”

“Voyager travels a million miles a day,” Stone said, “but a million miles out of a billion miles is a very tiny little sliver.”

The future is unknown

In terms of 2012 dollars, the two spacecraft and missions so far have cost taxpayers about $3.7 billion.

They have enough electrical power to last until 2020, Stone said. The team behind the spacecraft will begin to turn off instruments at that point to reduce power needs. The last instrument will likely be shut off in 2025.

“Then, they will orbit the center of our galaxy essentially forever,” he said.